The subject matter herein relates to distribution of electrical power across an integrated circuit chip through a power grid layer.
An integrated circuit (IC) chip typically includes one or two primary layers of electrical conductors (e.g. aluminum, copper and other conductors), a.k.a. a xe2x80x9cpower redistribution busxe2x80x9d or power distribution grid, that provide gross distribution of electrical power across the IC chip. The power distribution grid typically transmits the electrical power through other layers of electrical conductors that distribute the electrical power more finely to the various electronic components (e.g. transistors, capacitors, etc.) in the various other layers of the IC chip.
Examples of such power distribution grids 100, 102 and 104, specifically for wire bonded IC""s, are shown in FIGS. 1, 2 and 3, respectively. The power distribution grid 100 (FIG. 1) is similar to the grids 10 and 20 shown in prior art FIGS. 1 and 2 in U.S. Pat. No. 6,111,310. The power distribution grid 100 includes four main electrical conductors 106 arranged to form a square that generally corresponds to an outer perimeter of an IC (not shown) on which the power distribution grid 100 may be formed. The power distribution grid 100 also includes two sets of evenly spaced electrical conductors 108 and 110, one vertical set (electrical conductors 108) and one horizontal set (electrical conductors 110), that connect the main electrical conductors 106 on opposite sides of the outer perimeter of the IC. The electrical conductors 108 and 110 are generally perpendicular to each other and have a generally constant width. Additionally, the electrical conductors 108 are typically formed within a different layer of the IC than are the electrical conductors 110, so the electrical conductors 108 and 110 cannot intersect and cause an electrical short. Also, the electrical conductors 108 and 110 typically supply the electrical power to the IC, and another set of electrical conductors (not shown) disposed in the same two layers of the IC chip as the power electrical conductors 108 and 110 typically supplies the ground.
Since the electrical conductors 108 and 110 have a generally constant width, in order to deliver approximately the same current to each region of the IC chip, the current density must be considerably greater in the portion of the electrical conductors 108 and 110 near the periphery of the IC chip than in the center of the IC chip. The greater current density can result in electromigration if the cross-section of the electrical conductors 108 and 110 is too small near the periphery of the IC chip.
The power distribution grid 102 shown in FIG. 2 is similar to the power distribution grid 100 (FIG. 1) and to the grid 30 shown in FIG. 3 in U.S. Pat. No. 6,111,310. Similar to the power distribution grid 100, the power distribution grid 102 includes four main electrical conductors 112 arranged to form a square that generally corresponds to an outer perimeter of an IC (not shown) on which the power distribution grid 102 may be formed. The power distribution grid 100 also includes two sets of non-intersecting electrical conductors 114 and 116 that connect the main electrical conductors 112 on opposite sides of the outer perimeter of the IC chip. The electrical conductors 114 and 116 are generally perpendicular to each other. However, unlike the power distribution grid 100 shown in FIG. 1, the electrical conductors 114 and 116 have a varying width, instead of a constant width. In this manner, the problem with electromigration that may be experienced in the power distribution grid 100 is reduced in the power distribution grid 102. Additionally, the power distribution grid 102 exhibits less voltage drop than does the power distribution grid 100, so the power is more evenly distributed across the power distribution grid 102 than across the power distribution grid 100. The power distribution grid 102 is typically made from conductor material, such as aluminum, that can be formed in relatively wide lines.
The power distribution grid 104 shown in FIG. 3 is similar to the power distribution grid 102 (FIG. 2), except that the four main electrical conductors 118 (arranged to form a square that generally corresponds to an outer perimeter of an IC) and the two sets of non-intersecting variable-width conductors 120 and 122 are formed from multiple individual generally-constant-width electrical conductors 124. Having multiple individual electrical conductors 124 allows the power distribution grid 104 to be formed from conductor material, such as copper, that cannot readily be formed in relatively wide lines. Some of the individual electrical conductors 124 extend all the way across the IC chip (not shown), while the others extend only part way from the periphery of the IC chip toward the center of the IC chip. In this manner, the problem with electromigration that may be experienced in the power distribution grid 100 (FIG. 1) is reduced in the power distribution grid 104, because there are more of the individual electrical conductors 124 to transfer the current near the periphery of the IC chip where there is more current in the power distribution grid 104 than near the center of the IC chip.
The power distribution grids 100 (FIG. 1), 102 (FIG. 2) and 104 (FIG. 3) require exclusive use of at least two layers of the IC chip, which takes up valuable space within the IC chip and limits the vertical thickness of at least one of these two layers (increasing the layer""s resistance), since a layer that is overlaid by another layer is inherently restricted in its vertical thickness due to physical limitations of chip fabrication processes. On the other hand, if the power distribution grids 100, 102 and 104 were made with only one set of electrical conductors (e.g. 108, 114 and 120) in only one layer of the IC chip, then the power distribution grids 100, 102 and 104 would receive current on only two sides of the IC chip, e.g. the top and bottom sides, which requires a relatively tight arrangement of power pins (not shown) on only two sides of the IC chip and results in an unsymmetrical voltage drop from a given point on the IC chip to the nearest main electrical conductor 106 (FIG. 1), 112 (FIG. 2) or 118 (FIG. 3) on the periphery of the IC chip.
It is with respect to these and other background considerations that the subject matter herein has evolved.
The subject matter herein involves a power distribution grid that is formed in only one layer of an IC chip (e.g. the top layer), includes power pins on all four sides of the IC chip and results in a symmetrical voltage drop and current density in both the horizontal and vertical directions across the IC chip for a relatively even power distribution. The IC chip is generally divided into quadrants, each including one corner (top-left, top-right, bottom-right or bottom-left) of the IC chip and about half of the two side edges (top, bottom, left side and right side) that form the corner. Electrical conductors for each quadrant of the power distribution grid are routed from the side edge on one side of the corner of the IC chip to the side edge on the other side of the corner. Generally, the electrical conductors do not intersect each other, so the electrical conductors can be formed in the same layer of the IC chip.
In a particular embodiment, the electrical conductors of each quadrant are routed in general L-shapes from one IC chip side edge of the quadrant to the other IC chip side edge of the quadrant on the other side of the corner of the IC chip, without intersecting each other. The L-shaped electrical conductor nearest the corner of the IC chip in the quadrant is the shortest electrical conductor in the quadrant, and the L-shaped electrical conductor nearest the center of the IC chip is the longest electrical conductor in the quadrant. Additionally, the power distribution grid is generally symmetrical about the center point of the IC chip. Additionally, every other one of the L-shaped electrical conductors in each quadrant may be power conductors separated by ground conductors, so that all four side edges of the IC chip may have power and ground pins, resulting in the symmetrical voltage drop and current density and the relatively even power distribution across the IC chip.